fix: prevent duplicated codebase indexing on VSCode restart

[roomote]

This PR fixes issue #5941 where the codebase was being re-indexed every time VSCode was restarted, even when a valid index already existed.

Problem

The code indexing system was not checking if an existing index with data was already present before starting a full re-index on every VSCode restart. This caused unnecessary CPU usage and delays for users.

Solution

1. Added a hasData() method to the IVectorStore interface to check if the collection contains any indexed data
2. Modified the orchestrator to check for existing index data before performing a full scan
3. Updated the manager initialization logic to only trigger indexing when necessary (configuration changes or first initialization)

Changes

• Added hasData() method to IVectorStore interface
• Implemented hasData() in QdrantVectorStore to check collection point count
• Modified CodeIndexOrchestrator.startIndexing() to skip full scan if valid data exists
• Updated CodeIndexManager.initialize() to better handle existing indexes
• Updated test mocks to include the new hasData() method

Testing

• All existing tests pass
• The fix has been tested locally and prevents re-indexing when a valid index exists
• File watcher still works correctly for incremental updates

Fixes #5941

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Important

Fixes issue #5941 by preventing unnecessary codebase re-indexing on VSCode restart through checking existing index data.

• Behavior:
  • Prevents unnecessary re-indexing on VSCode restart by checking existing index data.
  • CodeIndexOrchestrator.startIndexing() skips full scan if valid data exists.
  • CodeIndexManager.initialize() only triggers indexing when necessary.
• Interfaces:
  • Added hasData() method to IVectorStore interface.
  • Implemented hasData() in QdrantVectorStore to check collection point count.
• Testing:
  • Updated test mocks to include hasData() method.
  • Verified that re-indexing is skipped when a valid index exists.
  • Ensured file watcher still functions for incremental updates.

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[daniel-lxs]

This would not scan the codebase when the extension starts meaning any changes made while the service wasn't watching for file modifications will not be picked up and the indexing will become outdated.

The initial scan skips files that have no changes so this isn't necessary. The actual bug must come from somewhere else in the code so the issue #5941 needs proper scoping.